Here's a figure we use to decide if a swarm is likely the result of a fault creep event. It compares the shape of the moment-rate history (measured as skewness) versus the stress drop. Swarms that appear to be associated with creep events have small or negative skews and low stress drops, whereas ordinary aftershock sequences tend to have positive skews and stress drops in the 1-10 MPa range (this is the total moment of the sequence scaled by a rough estimate of the total seismogenic area of the fault). The recent Bombay Beach swarm looks a lot like other Salton Trough and EPR swarms, including the 2005 Obsidian Buttes swarm a little to the south that had a lot of shallow creep associated with it. -Emily Roland updated the plot this morning with clearer labels, etc.

This latest event seems to be on the same "ladder rung" that was active earlier today.

Caption: ----------- Overview of the March 24, 2009 M 4.8 earthquake sequence near Bombay Beach, California. Seismicity from 1984-2008 is shown as white symbols (scaled by magnitude; from Lin et al., 2007). The latest events are shown as red circles (precisely re-located as of 3/24/09 noon local time by Egill Hauksson of Caltech). The activity occurred near the intersection of the San Andreas fault and the northeastward projection of the Extra fault zone, near the northern end of the Brawley Seismic Zone. This area has been seismically active previously in Oct. 1999 (Hough and Kanamori, 2002) and Nov. 2001. It has also been noted as being potentially significant for future rupture of the southern San Andreas fault (e.g., Hudnut et al., 1989). Active faults are shown in red if they have ruptured historically (the Elmore Ranch fault zone broke in Nov. 1987, and the Coyote Creek fault broke in 1968). Also shown in orange are faults that have been mapped and that have exhibited triggered creep during regional earthquakes. These include the San Andreas fault and Extra fault zone [data of Susanne U. Janecke, unpublished mapping, Kirby 2005 MS thesis, and Kirby et al. (2007). Additional faults are being mapped.] Other features shown are volcanic centers (orange circles) and various mud pots, carbon dioxide vents (green symbols; from Lynch & Hudnut, 2008). References: ---------------- Hough, S. E., Kanamori, H., Source Properties of Earthquakes near the Salton Sea Triggered by the 16 October 1999 M 7.1 Hector Mine, California, Earthquake Bull. Seis. Soc. Amer., 92: 1281-1289, 2002. Hudnut, K.W., L. Seeber, and J. Pacheco, Cross-fault triggering in the November 1987 Superstition Hills earthquake sequence, southern California, Geophys. Res. Lett., v. 16, No. 2, pp. 199-202, 1989. Kirby, S.M., 2005, The Quaternary tectonic and structural evolution of the San Felipe Hills, California, [M.S. Thesis]: Logan, Utah State University, 182 p. Kirby, S.M., Janecke, S.U., Dorsey, R.J., Housen, B.A., McDougall, K., Langenheim, V., and Steely, A. Jan 2007, Pleistocene Brawley and Ocotillo formations: Evidence for initial strike-slip deformation along the San Felipe and San Jacinto fault zones, California: Journal of Geology, v. 115, p. 43-62. Lin, G., P. Shearer and E. Hauksson (2007), Applying a three-dimensional velocity model, waveform cross correlation, and cluster analysis to locate southern California seismicity from 1981 to 2005, J. Geophys. Res., 112, B12309, doi:10.1029/2007JB004986 Lynch, D. K. and K. W. Hudnut, The Wister Mud Pot Lineament: Southeastward Extension or Abandoned Strand of the San Andreas Fault? Bull. Seis. Soc. Amer., Vol. 98, No. 4, pp. 1720-1729, doi: 10.1785/0120070252, 2008

I haven't yet received any requests for media interviews, but sometimes I do from newspapers in the Inland Empire. If I am interviewed, is it ok to tell them what is stated above--that CEPEC met this morning and briefed Cal-EMA? I presume that is public information, but thought that perhaps I should check. Sally McGill

Many of you know more about this than me, but I was reminded of the similarities with the Superstition Hills and prior events on cross faults in 1987. I am attaching a couple of BSSA papers FYI. Ramon

Kate Hutton was on KFWB an hour-plus ago talking about this. She might have some pre-prepared comments that would make for a good starting point for an FAQ.

Mike - What happens when you click on the link "Read more about Field Coordination Plans"? It should take you to another page, which by clicking Edit at the top of the page will allow you to edit as necessary. I tried, but was not able to replicate your error. I checked the settings and they are currently set for edit privileges for everyone.

I've never looked into the Salton Sea scenario. I think Grahm Kent and the scripps group are looking into putting a lot of instruments in there for the 2010 active source experiment. It might be good to try and get some sort of open rapid response permit worked out after they've figured out what's required. These instruments usually go offshore and can just be deployed, so we don't have any sort of rapid response permitting set up. The pool was setup with the goal of responding to cascadia/aleution/Caribean subduction zone quakes.

The Clearinghouse appreciates all the cooperation from manager and staff of SCEC and the Pasadena USGS office operations. Good show.......

But will be winding down soon........RCL

[simulation] UNAVCO is responding to a request from SCEC on behalf of six SCEC-affiliated institutions: USGS UC Berkeley UC Riverside Harvey Mudd Arizona State Caltech 5 UNAVCO trucks are leaving Boulder as I type to deliver 25 campaign GPS systems to Indio, to arrive early Saturday afternoon at the pre-arranged meeting place. We are preparing an additional 20 systems for Rick Bennett to occupy points in the ECSZ in Joshua Tree N.P. early next week. Preliminary funding authorization has been procured from NSF-EAR and EarthScope by SCEC and UNAVCO directors. [/simulation]